Recently, a printed board (wiring board) mostly is designed with a CAD (Computer Aided Design) for printed board design using a computer (see, for example, Patent Document 1). In the design of a printed board using the CAD, while there are a number of portions that are automated, there also are portions that cannot be designed appropriately without a skilled designer.
Particularly, in printed board design of a high-frequency circuit, the interference between wires has a large influence on transmission characteristics. In order to predict this influence in the design stage, it is necessary to obtain the interference amount between wires by complicated calculation based on an electromagnetic analysis. However, in complicated wiring design including an asymmetric coupled line, it is difficult to obtain the interference amount between wires by calculation, and there are a number of cases where the interference amount actually cannot be calculated. Therefore, the interference amount between wires mostly is considered by so-called guesswork by a skilled designer, instead of an electromagnetic analysis. Furthermore, the fact is that a printed board is developed by trial and error without considering the interference amount between wires.
The case where the interference amount between wires is obtained by a conventional electromagnetic analysis will be described. FIG. 24(a) is a diagram showing an example of a wiring pattern in one of inner layers included in a multi-layered board. In the case where wires to be analyzed have, for example, a wiring pattern 1000 (i.e., a complicated wiring pattern to be used actually) shown in FIG. 24(a), the wiring pattern 1000 cannot be subjected to an electromagnetic analysis as it is. Thus, the overall wiring pattern 1000 is divided into a mesh shape as in a wiring pattern 2000 shown in FIG. 24(b). An analysis model in each divided cell is subjected to an electromagnetic analysis. Next, the interaction between the respective cells is calculated, whereby the overall electromagnetic analysis is completed. The interference amount between wires is obtained from the results of the overall electromagnetic analysis.
However, in the case where the wires to be analyzed have the complicated wiring pattern 1000 as shown in FIG. 24(a), the number of divided cells is enormous as shown in FIG. 24(b), and consequently, a great amount of calculation time may be required. Thus, there are a number of cases where an electromagnetic analysis may not be completed within an actual working time. Particularly, in the case of a most-advanced printed board, an electromagnetic analysis may not be completed in all the cases.
For example, according to the study by the inventors of the present application, in the case where a printed board to be analyzed is a multi-layered board of 8 layers, having a size of 40 mm×40 mm, the number of nets (the number of wires connecting components) included in the printed board is 550, and the number of vias electrically connecting layers is 5000, the following results are predicted.
More specifically, in the case of performing an electromagnetic analysis method based on a moment method using a Pentium (Registered Trademark) 4 processor with a 3 GHz operation and a 2 G-byte memory for a CPU, with respect to 20 frequency points, it was predicted that the physical memory amount to be required exceeds the memory amount of a computer. Therefore, under the above conditions, it was inferred that an analysis cannot be performed. Even if the limit of a memory amount can be solved, it was predicted that at least 500 hours are required in order to perform an analysis.
Furthermore, as the number of frequency points increases, a processing time or a processing data amount increases. In addition, an electromagnetic analysis needs to be performed every time a printed board is improved, instead of only once. Therefore, it is actually very difficult to obtain the interference amount between wires by an electromagnetic analysis, aside from a printed board with a very simple configuration.
In order to enhance an electromagnetic analysis method, an electromagnetic analysis method by the combination of a finite element method and a boundary element method has been disclosed (see, for example, Patent Document 2).
Patent Document 1: JP 10-214281 A
Patent Document 2: JP 11-296504 A